Measurement of uranium and fission products in a spent fuel sample using fiber-optic laser-induced breakdown spectroscopy

Batsaikhan, M.; Oba, Hironori*; Karino, Takahiro; Akaoka, Katsuaki; Wakaida, Ikuo*; Iwata, Yoshihiro; Sakamoto, Kan*

Journal of Analytical Atomic Spectrometry, 41(4), p.1324 - 1335, 2026/04

https://doi.org/10.1039/D5JA00451A

Numerical analysis of A and A value ratios for off-site transportation of small-amount of fuel debris retrieved from the Fukushima Daiichi Nuclear Power Station

Sakamoto, Masahiro; Okumura, Keisuke; Kanno, Ikuo; Matsumura, Taichi; Riyana, E. S.; Terashima, Kenichi; Kaneko, Junichi*; Mizokami, Masato*; Mizokami, Shinya*

Radioisotopes, 75(S-01), p.S-001_1 - S-001_5, 2026/04

https://doi.org/10.3769/radioisotopes.S-001

Challenge for screening of nuclear fuel debris by innovative spectral imaging and its verification by LIBS mapping (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; The University of Osaka*

JAEA-Review 2025-040, 111 Pages, 2025/12

JAEA-Review-2025-040.pdf:22.28MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2023. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2023, this report summarizes the research results of the "Challenge for screening of nuclear fuel debris by innovative spectral imaging and its verification by LIBS mapping" conducted in FY2023. The present study aims to develop a remote-sensing technique to identify the in-reactor materials by a combination of Hyper Spectral Imaging (HSI) and Laser Induced Breakdown Spectroscopy (LIBS). HSI analyzes spectral information of more than 100 colors, and is being applied to classify various materials. On the other hand, material composition cannot be directly evaluated by HSI. Therefore, we thought that the combination of HSI and LIBS could be an accurate and wide-ranging visualization technique. In order to demonstrate the HSI and LIBS, it is necessary to prepare standard materials that simulate in-reactor materials, and to acquire and accumulate training data on them. In this study, the University of Osaka is in charge of the preparation of standard materials and HSI data analysis, Nuclear Fuel Development (NFD) is in charge of the preparation of uranium bearing materials and HSI/LIBS measurements, and JAEA is in charge of LIBS development. On the UK side, the Univ. of Strathclyde, National Nuclear Laboratory (NNL), and Lancaster University participate in the joint research project. The compositions of the standard samples were determined from past experiments and thermodynamic calculation results. Several samples such as UO based composites and concrete were prepared. The HSI data were obtained using a hyperspectral camera installed in the NFD. For LIBS, we worked on the automatic optimization of focal distance as part of the development of remote operation technology.

Investigation of effects of nano interfacial phenomena on dissolution aggregation of alpha nanoparticles by using micro nano technologies (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Institute of Science Tokyo*

JAEA-Review 2025-026, 72 Pages, 2025/11

JAEA-Review-2025-026.pdf:7.97MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2023. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2022, this report summarizes the research results of the "Investigation of effects of nano interfacial phenomena on dissolution aggregation of alpha nanoparticles by using micro nano technologies" conducted in FY2023. To ensure the safety of retrieval and storage management of nuclear fuel debris generated by the Fukushima-Daiichi Nuclear Power Station accident, understanding of dissolution-denaturation behavior of the fuel debris alpha particles is one of the most crucial issues. This research aims to create novel microfluidic real-time measurement device for elucidating dissolution, aggregation, and denaturation processes of metal oxide nanoparticles under various solution environments, and clarify their nano-size and interfacial effects. In this year, we conducted bulk and micro dissolution tests of simulated fuel debris particles (UO mechanical-treated nanoparticles, UO chemical-treated nanoparticles, and (U,Zr)O nanoparticles), and successfully clarified that the effects of particle sizes, reaction times, and HO concentrations on the dissolution behavior of each nanoparticle. In particular, it was found that (U,Zr)O nanoparticles have different degrees of Zr catalytic reactions depending on HO concentrations, resulting in the generation of different amounts of gas and U. Moreover, we developed a new microfluidic device which enables to instantly react the nanoparticles with HO solutions, and determined dynamic aggregation and dissolution rates of the nanoparticles. The research was carried out in close collaboration with UK researchers, and achieved the expected goal of this year.

Novel mechanical manipulator for efficient fuel debris retrieval (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; The University of Tokyo*

JAEA-Review 2025-014, 86 Pages, 2025/09

JAEA-Review-2025-014.pdf:9.38MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2023. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2021, this report summarizes the research results of the "Novel mechanical manipulator for efficient fuel debris retrieval" conducted from FY2021 to FY2023. The present study aims to the development of a collision-tolerant robotic manipulator with the mechanical variable impedance actuators in an unknown environment. Another research target is the system architecture of an artificial intelligence-based control method for efficient exploration and decommissioning. In addition to conducting an investigation in the area deep inside the aperture, which has been difficult with conventional investigations, we aim to recover pebble-shaped fuel debris at the bottom of the pedestal using a gripper at the tip of the manipulator. We will establish a manipulator mechanism and remote-control system to cope with the environmental constraints inside the pedestal. This year focused on developing a manipulator navigation algorithm, evaluating control performance, and conducting on-site scenario demonstration experiments. Studies included building a driving model, designing a control algorithm, and assessing manipulator control performance, with comparisons to simulation models. Demonstration experiments were conducted at facilities like the JAEA Naraha Center for Remote Control Technology Development. The research was promoted in close collaboration with the UK team and external advisors, including bi-weekly meetings. At the end of the fiscal year, an oral presentation introducing the project was given at an international workshop organized by the University of Tokyo and Technical University of Munich (TUM).

Clarification of debris formation conditions on the basis of the sampling data and experimental study using simulated fuel debris and reinforcement of the analytical results of severe accident scenario (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; University of Fukui*

JAEA-Review 2025-007, 120 Pages, 2025/09

JAEA-Review-2025-007.pdf:8.13MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2023. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station (1F), Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2021, this report summarizes the research results of the "Clarification of debris formation conditions on the basis of the sampling data and experimental study using simulated fuel debris and reinforcement of the analytical results of severe accident scenario" conducted from FY2021 to FY2023. The present study aims to clarify the debris formation mechanism and utilize the results to refine the accident scenario. In the backward analysis of oxide debris formation, we prepared simulated fuel particles by the aerodynamic levitation method and ejection of melted oxides from a tungsten pipe with a small hole and summarized the relationship between preparation conditions and the properties of the particles. We also demonstrated the formation of simulated fuel debris obtained by the sampling in 1F and clarified the difference between the experimental results and thermodynamic calculation. From the estimation of mixing, melting and solidified states of metallic debris, it was found that the formation of thin reaction layer suppresses the damage of SUS in spite of Zr content around 1000 C, and we quantify the elution rate of BC and Zircaloy to the melted SUS. We extended reaction rate data between various pressure vessel with SUS and Zr and welding parts and suggested reaction rate equation for large scale experiment. We also estimated the failure behavior of lower plenum of pressure vessel and outflow behavior of melt. Furthermore, we estimated transition behavior of Uranium melt to metallic debris melt in the re-melting process of predropped metallic debris. As the experimental techniques in the future, we prepared the semi-melted debris from oxide and metals and analyzed the reaction products and discussed the formation of simulated debris with a small amount of uranium oxide using a CCIM furnace and the aerodynamic levitation method.

Fuel debris criticality analysis technology using non-contact measurement method (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Institute of Science Tokyo*

JAEA-Review 2025-010, 62 Pages, 2025/08

JAEA-Review-2025-010.pdf:3.63MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2023. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2021, this report summarizes the research results of the "Fuel debris criticality analysis technology using non-contact measurement method" conducted from FY2021 to FY2023. The purpose of research was to improve the fuel debris criticality analysis technology using non-contact measurement method by the development of the fuel debris criticality characteristics measurement system and the multi-region integral kinetic analysis code. It was performed by Institute of Science Tokyo, Tokyo City University, National Institute of Advanced Industrial Science and Technology, and Nagaoka University of Technology. We developed the fuel debris criticality characteristics measurement system which has a two layer structure surrounding a canister containing fuel debris fragments with He proportional counters. The operational validation and performance evaluation were performed on the developed detector system. We have demonstrated the feasibility and accuracy of measuring the amount of fissile material and water content. MIK2.0-MVP code, which can calculate fission reaction rate attributed to both prompt and delayed neutrons and also can take the movement of fuel debris into calculation, was developed. After parallelizing the tally process of C() function, MIK2.0-MVP code will be applicable to weakly coupled reactors which include moving fuel debris particles if a supercomputer will be used for the tally process of C() function and if the coupling of MIK2.0-MVP code with MPS will be weak.

Development of a theoretical scaling factor method for the inventory estimation of difficult-to-measure nuclide Cs-135 in fuel debris and radioactive wastes

Sakamoto, Masahiro; Okumura, Keisuke; Kanno, Ikuo; Matsumura, Taichi; Terashima, Kenichi; Riyana, E. S.; Kaneko, Junichi*; Mizokami, Masato*; Mizokami, Shinya*

Journal of Nuclear Science and Technology, 62(8), p.756 - 765, 2025/08

https://doi.org/10.1080/00223131.2025.2478926

Experimental investigation of nonisothermal interaction between Fe-Zr melt and stainless steel forming "metallic debris" in Fukushima Daiichi Nuclear Power Station

Ito, Ayumi*; Kanno, Tatsuya*; Iwama, Takayuki*; Ueda, Shigeru*; Sato, Takumi; Nagae, Yuji

Annals of Nuclear Energy, 217, p.111333_1 - 111333_14, 2025/07

https://doi.org/10.1016/j.anucene.2025.111333

In the Fukushima Daiichi Nuclear Power Station Unit 2, the formation of a metallic pool, mainly comprising Fe and Zr, has been proposed as a mechanism contributing to the failure of the reactor pressure vessel. This study focuses on material interactions during the early core degradation that led to metallic pool formation in the late phase of the in-vessel degradation process. Initially, two compositions, Fe-87Zr and Fe-15Zr (at%), were heated to the liquidus temperature of 1723 K, dropped onto SS at lower temperatures, and the metallographic structure of the reaction products was examined. Subsequently, the Fe-87Zr melt at temperatures ranging from 1723 to 1873 K was dropped onto oxidized SS to evaluate the influence of the oxide layer on degradation. This study confirmed that the liquidus temperatures of all intermetallic compounds were below 2000 K, and the metallic debris could be a source of the "metallic pool formation" predicted by recent severe accident analysis.

Development of a method for the determination of spontaneous fission nuclides in irradiated fuel and applicability to Pu quantification in fuel debris by dual time neutron measurements

Nagatani, Taketeru; Kosuge, Yoshihiro*; Sagara, Hiroshi*; Nakaguki, Sho; Nomi, Takayoshi; Okumura, Keisuke

Progress in Nuclear Science and Technology (Internet), 7, p.41 - 46, 2025/03

https://doi.org/10.15669/pnst.7.41